Support absolute url to override base url

CHANGES/10074.feature.rst

@@ -0,0 +1,2 @@
+Added support for overriding the base URL with an absolute one in client sessions
+-- by :user:`vivodi`.

CONTRIBUTORS.txt

@@ -54,6 +54,7 @@ Arseny Timoniq
 Artem Yushkovskiy
 Arthur Darcet
 Austin Scola
+Bai Haoran
 Ben Bader
 Ben Greiner
 Ben Kallus

aiohttp/client.py

@@ -414,11 +414,8 @@ def request(
 
     def _build_url(self, str_or_url: StrOrURL) -> URL:
         url = URL(str_or_url)
-        if self._base_url is None:
-            return url
-        else:
-            assert not url.absolute
-            return self._base_url.join(url)
+        need_join = self._base_url and not url.absolute
+        return self._base_url.join(url) if need_join else url
 
     async def _request(
         self,

docs/client_reference.rst

@@ -79,6 +79,10 @@ The client session supports the context manager protocol for self closing.
 
       .. versionadded:: 3.8
 
+      .. versionchanged:: 3.12
+
+         Added support for overriding the base URL with an absolute one in client sessions.
+
    :param aiohttp.BaseConnector connector: BaseConnector
       sub-class instance to support connection pooling.
 

tests/test_client_session.py

@@ -1140,6 +1140,24 @@ async def test_requote_redirect_url_default_disable() -> None:
             URL("http://example.com/test1/test2?q=foo#bar"),
             id="base_url=URL('http://example.com/test1/') url='test2?q=foo#bar'",
         ),
+        pytest.param(
+            URL("http://example.com/test1/"),
+            "http://foo.com/bar",
+            URL("http://foo.com/bar"),
+            id="base_url=URL('http://example.com/test1/') url='http://foo.com/bar'",
+        ),
+        pytest.param(
+            URL("http://example.com"),
+            "http://foo.com/bar",
+            URL("http://foo.com/bar"),
+            id="base_url=URL('http://example.com') url='http://foo.com/bar'",
+        ),
+        pytest.param(
+            URL("http://example.com/test1/"),
+            "http://foo.com",
+            URL("http://foo.com"),
+            id="base_url=URL('http://example.com/test1/') url='http://foo.com'",
+        ),
     ],
 )
 async def test_build_url_returns_expected_url(